Olefin polymerizations such as ethylene polymerization are frequently carried out using monomer, diluent and catalyst and optionally co-monomers and reaction additives like anti-fouling in a loop reactor. The polymerization is usually performed under slurry conditions, wherein the product consists usually of solid particles and is in suspension in a liquid medium containing diluent, monomer and the optional co-monomer and reaction additives (in short the diluent). The slurry content of the reactor is circulated continuously with a pump to maintain efficient suspension of the polymer solid particles in the liquid diluent, the product being often taken off by means of settling legs, which often operate on a batch principle to recover the produce when the reactor is the sole reactor of the polymerization process or when it is the last reactor of a series of reactors in the polymerization process, the product is further discharged to a flash tank, through flash lines, where most of the diluent and unreacted monomers are flashed off and recycled. The polymer particles are dried, additives can be added and finally the polymer is extruded and pelletized. When the reactor is in series with at least another consecutive reactor in the process of polymerization, the product is further discharged to a transfer line in connection with said other reactor. This technique has enjoyed international success with millions of tons of ethylene polymers being so produced annually.
Reversing the definition of residence time, the production of a polymer from a given reactor can be described as the ratio between the quantity of polymer contained in the reactor to the polymer average residence time in the reactor. Well-known methods to increase production often imply the reduction of the residence time, which unfortunately modifies the properties of the polymer. Other ways to increase production are associated with the increase of polymer quantity in the reactor, this means for a given fixed reactor size, the concentration of solids in the reactor.
Commercial production of olefin polymers such as ethylene polymers in isobutane diluent has historically been limited to a maximum solids concentration in the reactor of 37-40 weight % for high density ethylene polymers with values as high as 42-46 weight % possible with several process enhancements. Above the mentioned concentration levels, instabilities arise inside the reactor and force to reduce the solids concentration. Whatever the maximum for a given set of process conditions, improvement in solids concentration is still required.
In homogeneities inside the reactor are detrimental to the achievable production because instabilities tend to be initiated locally at the high concentration locations and then do propagate inside the whole reactor.
It is therefore an object of the present invention to improve the homogeneity of the slurry circulating inside the reactor. It is another object of the present invention to increase the solids content of polymer in the reactor. It is yet a further object to optimize the distribution and mixing of the reactants of a polymerization reaction in a reactor.